The present invention relates generally to ceramic matrix composite materials, and more specifically to a method and apparatus for arresting cracks within ceramic matrix composite materials.
Gas turbine engines typically include a compressor, a combustor, and a turbine. Airflow entering the compressor is compressed and channeled to the combustor, wherein the air is mixed with a fuel and ignited within a combustion chamber to produce combustion gases. The combustion gases are channeled to a turbine that extracts energy from the combustion gases for powering the compressor. One turbine extracts energy from the combustion gases to power the compressor. Other turbines may be used to power an output shaft connected to a load, such as an electrical generator. In some applications, the combustion gases exiting the turbine(s) are channeled through an engine exhaust nozzle to produce thrust for propelling an aircraft in flight.
Some known gas turbine aircraft engines include an engine exhaust nozzle having a variable geometry configuration, wherein a cross-sectional area of the exhaust nozzle is adjustable. Variable geometry exhaust nozzles typically have a plurality of flaps and a plurality of seals mounted circumferentially about a centerline of the exhaust nozzle. The seals are mounted generally between adjacent nozzle flaps, such that the flaps and seals form a generally continuous interior surface that directs a flow of the combustion gases through the exhaust nozzle. As their name implies, the seals seal the spaces between the flaps and shield various components of the exhaust nozzle from high temperatures and high thermal gradients during flow of the combustion gases therein.
To facilitate extending a useful life at high temperature operation, some seals are fabricated from non-metallic composite materials, such as ceramic matrix composite materials. However, even such non-metallic materials experience wear and other damage due to the hostile operating environment in gas turbine engines. For example, cracks may develop within the seals because of the high thermal gradients the seals experience during operation. Known methods for repairing such cracks typically include replacement of the seal with an undamaged seal, or replacement of a portion of the seal with undamaged material. However, replacement of a seal or a portion thereof can be costly and may result in disposal of seals still having a useful operational life.